Toona ciliata var. pubescens, known as “Chinese mahogany”, has high commercial value and is classified as a level II priority protected wild plant in China. However, due to overexploitation and its poor natural regeneration capacity, natural T. ciliata var. pubescens forests show varying degrees of decline in habitat adaptability. Arbuscular mycorrhizal fungi (AMF) symbiosis presents a potential strategy to enhance its regeneration. In this study, T. ciliata var. pubescens seedlings were inoculated with Septoglomus viscosum, followed by RNA-Seq analysis to compare gene expression differences between AMF-inoculated (AMI) and non-mycorrhizal (NM) treatments three months post-inoculation. A total of 16,163 differentially expressed genes (DEGs) were upregulated by AMF colonization, constituting 96.46% of the total DEGs. Specifically, 14,420 DEGs were exclusively expressed in the AMI treatment, while 35 DEGs were completely silenced. Most of the upregulated DEGs were located on the cell membrane, nucleus, and cytoskeleton and functioned in protein binding, S-adenosylmethionine-dependent methyltransferase activity, and lipid binding during cellular/macromolecule/protein localization, intracellular/protein transport, the cell cycle, and signal transduction. Additionally, lots of key genes related to oxidative stress responses, nutrient transport, and small GTPase-mediated signal transduction were found to be upregulated. These results suggest that AMF inoculation may enhance root cell growth by activating genes involved in nutrient uptake, stress responses, signal transduction, and substance transportation. This study elucidates the molecular mechanisms underlying the growth promotion of T. ciliata var. pubescens through AMF symbiosis, laying a foundation for the future application of AMF in its natural forest regeneration.

The aspect can affect plant communities and soil physical and chemical properties through different microclimates. However, little is known about the effect of aspect on arbuscular mycorrhizal (AM) fungal diversity and community composition, although AM fungi are beneficial for plant nutrient absorption and natural restoration. In this study, AM fungal community and diversity distribution patterns in the rhizosphere soil and roots of seven widespread plants in a natural Toona ciliata var. pubescens (Tc) forest on the north-facing (NF) aspect and south-facing (SF) aspect were investigated using Illumina PE250 high-throughput sequencing in the Guanshan National Nature Reserve, Jiangxi Province, China. Our results exhibited that aspect did not affect AM fungal diversity but significantly affected AM fungal community structure and composition. Glomeraceae was the most common and abundant family in the Tc natural forest. The Glomeromycota sequence proportion of root AM fungal community was significantly larger on NF than on SF (p < 0.05). The relative abundance of Acaulosporaceae of root AM fungal community differed significantly with aspect, being greater on NF than on SF (p < 0.05). In addition, the number of Glomeromycota sequences was significantly larger on SF than on NF, while the number of OTUs and the relative abundance of unclassified fungi in rhizosphere soil in Tc showed the opposite trend (p < 0.05). The soil properties (organic matter, nitrogen, potassium, phosphorus, and pH) were significantly correlated with these changes. These findings indicate that the habitat of NF with low insolation, high soil moisture, and high nutrient content might promote the functional realization of AM fungi; the habitat of SF with high insolation, low soil moisture, and low soil nutrient content might be beneficial for the proliferation and preservation of AM fungal groups. This study provides important information on the ecological processes of AM fungal community construction and microbiological mechanisms in natural Tc forests.

Toona ciliata var. pubescens ( Toona in Meliaceae) ( Tc ) is listed as an endangered species, and there are natural regeneration obstacles due to its long-term excessive exploitation and utilization. Arbuscular mycorrhizal fungi (AMF) can produce beneficial effects for plant growth and natural regeneration. However, the characteristics of the AMF community in natural Tc forests are poorly understood. The Illumina PE250 high-throughput sequencing method was used to study the characteristics of the AMF community in the rhizosphere soil and roots associated with three dominant tree species ( Tc ; Padus buergeriana , Pb ; and Maesa japonica , Mj ) in a natural Tc forest in Guanshan National Natural Reserve, South Central China. The results found that Glomeraceae was the most abundant AMF family in the rhizosphere soil and roots. Moreover, the relative abundance of Archaeosporaceae in rhizosphere soil was significantly larger than that in the roots; in contrast, the relative abundance of Glomeraceae in rhizosphere soil was significantly lower than that in the roots ( p < 0.05). Regarding different tree species, the relative abundances of Acaulosporaceae and Geosiphonaceae were larger in Mj and Tc than in Pb . AMF operational taxonomic units (OTUs) were 1.30-, 1.43-, and 1.71-fold higher in the Tc , Pb , and Mj rhizosphere soil, respectively, than in the corresponding roots. Nevertheless, higher AMF community richness was found in the roots compared to that in the rhizosphere soil based on the Chao index. This finding indicated that AMF of a relatively high aggregation degree were in roots, and more AMF groups with relatively low abundance occurred in the rhizosphere soil, which correspondingly lowered the calculated richness index of the AMF community. A redundancy analysis showed that different soil chemical properties impacted variations in the AMF community characteristics differently. This study has great significance for the interpretation of AMF diversity survey and the application design of AMF in vegetation restoration.